ISLAMABAD, Pakistan (CNN) --The man believed to be the key planner of the terrorist attacks of September 11, 2001 -- and several al Qaeda attacks in the past five years -- was among three terrorism suspects arrested in a CIA-led operation early Saturday in a house outside the Pakistani capital.

The arrest of Khalid Shaikh Mohammed is the single most important in the war on terror since September 11, said a law enforcement official close to the investigation.

He was arrested along with a Pakistani political leader, Ahmed Abdul Qadoos, and a man of Middle Eastern origin, Pakistani government officials said.

Mohammed was no longer in Pakistan as of late Saturday, the officials said. It was not known where Mohammed was or who had custody of him.

The law enforcement official said the operation was "ongoing" but that it was unclear whether specific intelligence led to the arrest or whether Mohammed was captured as part of a broader operation.

Mohammed was almost picked up last week in Quetta, Pakistan, 400 miles away from the Islamabad suburb where he was captured. Officials in Quetta picked up one suspected al Qaeda operative, but Mohammed escaped, according to highly placed Pakistan officials. Using the captured suspect, officials tracked Mohammed to the house in the middle class suburb of Rawalpindi, nine miles southeast of Islamabad.

A leader of Pakistan's largest religious political party, Jamaat Islami, lives in the house where Mohammed was captured. The group has not taken a formal stance on al Qaeda, but it has condemned the U.S. presence in Pakistan.

$25 million reward

The White House commended the arrests, calling Mohammed one of Osama bin Laden's "most senior and significant lieutenants, [and] a key al Qaeda planner and the mastermind of the September 11th attacks."

The U.S. State Department had offered up to $25 million for information leading to Mohammed's arrest.

Notified Saturday at 7 a.m. that Mohammed had been captured, President George Bush said, "that's fantastic."

White House spokesman Ari Fleischer said Mohammed was central to al Qaeda's ability to plan and carry out operations.

"You cannot overstate the importance of this," Fleischer said. "It is a good day, a big day."

Fleischer said the capture sends two messages: One, to the families of September 11 victims, that the mastermind of the terrorist attacks has been caught; and two, to al Qaeda: "It's only a matter of time before we get you."

There are no plans at this point to bring Mohammed to the United States, U.S. government officials said.

They confirmed that Mohammed is no longer in Pakistan and is being taken to an undisclosed location.

Mohammed's al Qaeda roots run deep and wide. One senior government official characterized the breadth of Mohammed's involvement by describing him as the Forrest Gump of al Qaeda, in reference to the book and movie character who appeared in critical moments in recent U.S. history.

Mohammed was indicted in 1996 in the Southern District of New York for his alleged role in a Philippines-based plot to blow up 12 U.S.-bound commercial airliners within 48 hours. The indictment has no immediate legal bearing, U.S. government officials said; the priority is to interrogate him.

Terrorism expert: Suspect ordered journalist's murder

Rohan Gunaratna, a terrorism expert and author of "Inside Al Qaeda," said Mohammed ordered the killing of Wall Street Journal reporter Daniel Pearl. Pearl, 38, was kidnapped in Karachi, Pakistan, in January 2002 while researching Pakistani extremist groups for an article. A grisly videotape received by U.S. diplomats February 21 of that year showed Pearl's murder.

STATEMENT

White House reaction to the detention of Khalid Shaikh Mohammed:"The United States commends Pakistani and U.S. authorities on the completion of a successful joint operation which resulted in the detention of several al Al Qaida operatives, including Khalid Shaikh Mohammed."Khalid Shaikh Mohammed is one of Usama Bin Laden 's most senior and significant lieutenants, a key Al Qaida planner and the mastermind of the September 11th attacks. He is known to have been centrally involved in plotting by Al Qaida terrorists since September 11th, 2001--including plots to launch attacks within the United States."Khalid Shaikh Mohammed is on the FBI's list of most wanted terrorists, and has been under U.S. indictment since 1996 for the Manila air conspiracy, a plot to bomb a series of U.S. civilian airliners."

"Daniel Pearl was going in search of the al Qaeda network that was operational in Karachi, and it was at the instruction of Khalid Shaikh Mohammed that Daniel Pearl was killed," Gunaratna said.

Mohammed has been linked to the bombing of the USS Cole in 2000, Richard Reid's foiled 2001 attempt to blow up an airliner with a shoe bomb, and most recently, the bombings at the El Ghriba synagogue in Djerba, Tunisia, that killed 19 last year.

The synagogue bombings were the first successful al Qaeda attacks outside Afghanistan after September 11, 2001, when terrorists hijacked four airlines and crashed them into the World Trade Center, the Pentagon and a field in Pennsylvania, killing more than 3,000 people.

In September, Yosri Fouda, a reporter for the Arabic-language Al-Jazeera television network, said he interviewed Mohammed while making a documentary for the first anniversary of the September 11 attacks.

Fouda said Mohammed introduced himself as the head of the al Qaeda military committee. He told Fouda, complete with details, that he attended the meeting during which the decision was made to strike at America inside America.

U.S. and coalition intelligence confirmed Mohammed's presence at the meeting.

Mohammed was indicted in 1996 for his alleged role in the airliner plot led by his nephew, Ramzi Yousef. Mohammed's indictment and federal arrest warrant, unsealed after Yousef's sentencing in 1998, provide details of the plot and how Mohammed allegedly operated within al Qaeda.

Yousef rented an apartment in Manila, according to the indictment. Yousef and Mohammed, who used the name Salem Ali, lived there mixing chemicals for explosives. They also had "modified timing devices," according to the indictments.

The airliner plot, nicknamed "Bojinka," which roughly translates to "explosion" in Serbo-Croatian, was uncovered in January 1995 when Mohammed's apartment caught fire.

Also in the computer were a communication signed by "Khalid Shaikh" and a letter, apparently related, that threatened to attack American targets "in response to the financial, political and military assistance given to the Jewish state in the occupied land of Palestine by the American government."

The letter, apparently written by Mohammed and his associates, also threatened to assassinate the president of the Philippines, attack aircraft, or even launch a biochemical attack if one of their co-conspirators was not released from custody.

Yousef was caught in Pakistan in February 1995. Mohammed was indicted on seven counts of terror conspiracy for his role in the plot.

Alleged al Qaeda planner

U.S. and Canadian intelligence documents based on the interrogation of Mohammed Mansour Jabarah, an al Qaeda operative who reported to Mohammed, show the level of detail and planning involved in an al Qaeda attack.

Mohammed sent Jabarah from Pakistan to southeast Asia on September 10, 2001, the day before the attacks on the World Trade Center and the Pentagon, according to the documents.

Jabarah was to lay the groundwork for suicide truck bombing runs on U.S. and British embassies in Singapore, Indonesia, and the Philippines on September 11, 2002.

The plan was foiled after a terrorist cell in Singapore was broken up. Jabarah was arrested in March and is in U.S. custody.

The Pentagon lauded the news of Mohammed's arrest in Pakistan.

"The government of Pakistan continues to be supportive in its effort to stop terrorists around the world, and we hope that continues," spokesman Sgt. Maj. Lewis Matson said. "The U.S. took a big hit a year and a half ago on September 11. We certainly haven't forgotten that at U.S. Central Command. We're glad a lot of other people recognize that too."

Fleischer said Mohammed's arrest had nothing to do with the lowering of the nation's threat level from orange to yellow Thursday. The information about the arrest came after the Homeland Security Department made the decision to lower it, he said.

Mohammed was born in Kuwait either March 1, 1964 or April 14, 1965. He carries a Pakistani passport.